Our understanding of human cytomegalovirus (HCMV) infection has been enhanced by discovery of a 2nd pathway of virus entry into epithelial-endothelial cells (Epi/EC) mediated by a pentameric virion glycoprotein complex. The culmination of many years of study on the original Fibroblast (Fibro) pathway of HCMV entry was a clinical trial in which a formulated gB vaccine was repeatedly administered to HCMV-negative women and 50% protection against primary infection was found. We have reproduced this success using Rhesus CMV (RhCMV)-negative rhesus macaques (RM) by demonstrating 50% protection against a virulent RhCMV challenge, using a modified vaccinia Ankara (MVA) vaccine composed of RhgB and the tegument protein Rhpp65. We hypothesize that to further improve vaccine success; efficient inhibition of CMV entry into Epi/EC will be required. Utilizing a revolutionary approach of manipulation of a bacterial artificial chromosome (BAC) derived MVA, we serially cloned each of 5 subunit proteins constituting the RhCMV UL128C (RhUL128C) in separate MVA insertion sites in a BAC plasmid. We recently published that vaccination of RhCMV-negative RM with RhUL128C-MVA produced high titer neutralizing antibodies (NAb) that inhibit virulent RhCMV natural isolates from infecting Epi/EC and Fibro, confirming RhUL128C function. Based on these novel results in the RhCMV/RM model, we constructed an HCMV counterpart to RhUL128C in BAC-MVA, and the reconstituted MVA virus used to vaccinate BALB/c mice generated NAb to prevent in vitro HCMV infection of Epi/EC. The following 3 Specific Aims (SA) will test this concept forming a path to clinical evaluation. In SA1 we will clone MVA (1974-MVA) into a self-excisable BAC, followed by insertion of 5 subunit genes constituting HCMV UL128C (H-UL128C) to construct a functional vaccine. H-UL128C expressed from MVA will be functionally evaluated by measuring direct in vitro inhibition of HCMV infection of Epi cells (ARPE-19), and indirectly by in vivo generation of NAb in BALB/c mice that will inhibit HCMV infection of ARPE-19 cells. In SA2, H-UL128C- MVA will be used to vaccinate RM and properties of NAb generated against the pentamer complex in sera and saliva from vaccinated and control groups will be assessed in preventing natural HCMV isolate infection of ARPE-19 cells. Avidity assays of post-vaccination sera will be assessed using urea denaturation after binding to pentamer containing lysates. In SA3 we will choose a regimen for inhibition of 2 HCMV entry pathways by including vaccines expressing H-UL128C and HCMV pp65/gB subunits either as 2 individual vaccines or a single multiple insert form. Preliminary studies in BALB/c mice will allow down-selection of better performing constructs. The formulation and regimen will be selected based on generation of superior NAb avidity and titers that interfere with in vitro HCMV infection of ARPE-19 cells and Fibro. Assessment of cytolytic recognition of rAdv-infected blasts and T cell activation will be 1st conducted in vaccinated mice, then RM in SA2 & 3. The anticipated result of these studies will be an HCMV-based subunit vaccine ready for clinical development.